(1) Field of the Invention
This invention relates to a liquid pigment composition for master-coloring (i.e., spin-dyeing) polyamides, and to a master-colored polyamide yarn made by master-coloring a polyamide with the same. More particularly, the present invention relates to a liquid pigment having a good compatibility with a polyamide, and also to a master-colored polyamide yarn made by using this liquid pigment.
(2) Description of the Related Art
In general, master-colored yarns have been valuably used for ordinary clothing and industrial materials widely in various fields because of the merit that the subsequent dyeing step can be omitted. In addition, master-colored yarns have an excellent weathering fastness and therefore the demand for master colored yarns has recently been increasing.
In the field of ordinary clothing and industrial materials, master-colored polyamide yarns are seldom used with a single color alone, and various kinds of master-colored yarns having different colors are required. As the means for satisfying this requirement, there has been adopted a method of adding a master batch of a coloring material to a polyamide.
This master batch addition method requires, however, cleaning of a material supply system and washing of an extruder and conduits at the step of changeover of the color, and the master batch addition method has a problem in that the productivity is inevitably reduced.
A proposal of an injection method has been made mainly on polyester fibers, instead of the master batch addition method. In the injection method, a liquid pigment dispersant (colorant) is supplied from the midway of a melting apparatus so as to effect the changeover without contamination of the extruder with the pigment dispersant (see, for example, Japanese Unexamined Patent Publication No. 58-149311, 60-45689, 60-45690, 63-92719 and 63-117071).
Liquid pigment dispersants described in these prior art references are liquid at normal temperatures, and low-molecular-weight polyesters and polyethers having a number average molecular weight of 1,000 to 4,000 are specifically mentioned as examples. These liquid pigment dispersants are, however, used exclusively for polyesters and polypropylene, and if these dispersants are incorporated in polyamides, since these dispersants have a polarity different from that of polyamides, the dispersants separate from the polyamide at the melt spinning step, i.e., bleed out, and bending of the filamentary extrudate occurs, with the result that no satisfactory operational perfarmance is attained.
Another proposal has been made in which a pigment dispersant of a liquid polyether or polyether-ester type having a hydroxyl value (OH value) below 25 mg KOH/g and thus an improved heat resistance is used for master-coloring polyesters (see Japanese Unexamined Japanese Patent Publication No. 63-120767 and 01-118678). Where this pigment dispersant is used for master-coloring polyamides, since the dispersant has no compatibility with polyamides, the dispersant separates from the polyamides and is difficult to add in an amount sufficient for the master coloration, and therefore, the dispersant of this type is of no practical use for master-coloring polyamides.
Still another proposal has been made in which a liquid pigment dispersant comprised of an isoindolinone pigment and a metal salt of stearic acid is used for master-coloring polyamides (see Japanese Unexamined Patent Publication No. 63-92717). This particular liquid pigment dispersant cannot widely be applied to polyamides.
A further proposal has been made in which a liquid pigment dispersant comprising a low-molecular-weight polyamide dispersant and having a good compatibility with a polyamide is used for master-coloring a polyamide. The liquid pigment dispersant of this type does not have a heat resistance sufficient to resist the melt spinning and is of no practical use.
More specifically, a liquid pigment dispersant to be used exclusively for polyamides has heretofore not been developed, as set forth on page 2, right upper column, lines 5-8 of Japanese Unexamined Patent Pulication No. 63-92717, and at present a colored polyamide yarn is not commercially produced, which is master-colored with a liquid pigment commercially available for master coloration of polyamides.